Mosquito-borne diseases, biodiversity and global change
1. Relevance of MBs
Most prevalent in the Southern hemisphere
1 million deaths/year - within Malaria causing the largest burden on a global-scale
DENV causes more cases/year (390 mill) than malaria (207 mill) but result in less fatal cases
Global burden has a socio-economical impact on society (ranges from 1000 to billions of dollars). Why?
❖ Missed time at work → less productivity
❖ Medical treatment or hospitalisation bills
❖ Transportation cost for doctor’s visits and related travel
❖ Costs of Vector control measures e.g., insecticides, sprays to prevent further bites
❖ Public prevention and health programs (educational purposes)
❖ Vaccine programs
❖ Compensation for businesses and communities affected by epidemics or outbreaks
❖ Research
2. Mosquito associated pathogens
Anopheles: Plasmodium falciparum, P. malariae, P. ovale and P. vivax, O’Nyong Nyong (ONN)
Culex: Japanese Encephalitis (JE), West Nile (WN), Saint Louis Encephalitis(SLE), RiftValley Fever (RVF); Sindbis (SIN)
Aedes: Dengue (DEN), Chikungunya (CHIK), Zika (ZIKA)
Sandflies: Phlebotomus fever (Leishmania)
Ticks: Tick-borne encephalitis (RSSE,OMSK, CEE, POW, KFD...); Crimean Congo Hemorrhagic fever (CCHF)
DENV CHIKV
Hotspots located in (sub)tropical regions Underreported
Often misdiagnosed with malaria or ZIKA Widespread phenomenon
Aedes spp Aedes spp
ZIKA JEV
Mostly located in Africa, Asia & South-America Complex life cycle including
Aedes spp (different subspecies depending on biotope) ❖ Mosquito
Sylvatic & urban cycle ❖ Waterfowls, pigs
Sexual + congenital transmission and blood transfusion ❖ Humans
WNV + EEE
Bird sylvatic cycle
Human & horses = dead-end hosts (no pathogen replication)
3. Vector ecology & prominent vectors
Anopheles life cycle :
💠
1. Adult or imago
💠 Mainly feeds on sugar as energy source
Only females feed on blood for egg prod.
2. Egg (on water surface)
3. Multiple larval stages
4. Pupa
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, Anopheles gambiae (s.l.)
Most important vector for P. falciparum (Malaria) ⇒ so-called “deadliest animal in the world”
An. gambiae refers to a complex: An gambiae s.s., An funestus, etc
Location: mostly in eastern Africa
Habitat
❖ Some subspecies prefer to live near houses (~higher risk of disease transmission), others prefer the forest (~lower risk)
❖ Sunlit pools
❖ Pioneer species which rapidly colonise recently flooded fields, decline as crops grow (cover water surface), often
man-made breeding sites (old tires) and anthropophilic (An. gambiae s.s. >> An. arabiensis)
Aedes albopictus
Morphology: one white vertical line on thorax
Origin: Asia (hence: Asian Tiger Mosquito, zoophilic forest species)
Temp: tolerates lower temperatures (except Antarctica)
Transmits: arboviruses e.g., DENV, ZIKA, CHIKV, EEE, …
Habitat (peri-domestic habitats & surrounding natural habitats)
❖ Larva: man-made containers
❖ Adult: urban or peri-urban (near houses) or surrounding natural habitats
Diapause: eggs (a period of suspended development in an insect, especially during unfavourable environmental condition)
Generalist: tropical species that adapted itself to temperate regions e.g., Europe (emergence from South to North)
Exophagic/philic (bites and lives outside)
Bites humans & animals opportunistically in daylight hours (host availability)
Aedes aegypti
Morphology: striped pattern on thorax
Origin: Africa
Temp: (sub)tropical regions
Transmits: arboviruses e.g., DENV, ZIKA, CHIKV, EEE, YFV, …
Habitat (Africa ancestral form: zoophilic tree hole mosquito Ae. aegypti formosus)
❖ Breeding places: water containers close to or in houses/stables
❖ Larva: man-made containers
❖ Adult: urban or domestic
Anthropophagic (feeds exclusively on humans) during daylight
Endophilic (lives nearby or in houses)
Density indexes: (don’t know by heart)
❖ Bretau index: n°r of positive containers per 100 houses
❖ House index: % positieve houses
❖ Container index: % of water receptacles containing Aedes
❖ Stegomyia index: n° of positive containers per 1000 persons
❖ Adult productivity index: sum containers type x mean larvae
❖ Ratio pupae/person
4. Vectors & climate change
Predicted global geographical distribution of Ae. aegypti and Ae. albopictus at different RCP scenarios
❖ At the moment between RCP 6.0-8.5
❖ Suspected that % of increase in population at risk will become larger and larger over the next decennia (2050, 2080)
Life-table data & modelling: Ae japonicus
❖ Experimental life-table data feed models for calculating population dynamics & climatic suitability indices
❖ Cumulative female survival [1/day] at a peak level around 25°C (= optimum Temp)
○ With a sudden decrease at higher temperatures
❖ Estimation of the n° of potential generations per year with a low greenhouse gas emission model (not realistic anymore)
○ Ae japonicus is invasive in Europe (only a few hotspots)
○ Suspected that around 2041-2060 the n° of generations per year in whole Eu will be between 6-7
Impact on climate change: climate, travel, trade and adaptation !
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,Climate sustainability is concerned with protecting the planet, halting climate change and promoting social development, without
endangering life on Earth or leaving anyone behind.
❖ It is used as an ecological modelling approach to assess disease vector species’ potential disruptions and evaluate the
Malaria transmission risk.
❖ Ecological modelling and practice can be different e.g., people may start to collect more water because of increasing T
(global warming), which increases the n° of potential breeding spots for the mosquitoes
Complex interplay of mosquito borne diseases, biodiversity and global changes:
Mosquito-borne diseases & climate change ?
❖ “Insect-borne disease are not disease of climate but of poverty” (Statement Reiter)
❖ Agree? Disagree? Statement is only focus on the money aspect
❖ It is really a interplay of climate, mosquito biology with social and political factors (PWEVVR)
○ Political stability
○ Good water service
○ Education programs
○ Vector control measures
○ Vaccine, public prevention and-health programs
○ Research
5. Aim of this lesson
1. State at least 5 MBDs.
❖ Malaria, Dengue, Zika, EEE/WEE and CHIKV
2. List three prominent MBD vectors + see information “Summary poster & traps.pptx”
❖ An gambiae (for Malaria) - endophilic, endophagic, anthropophagic, nocturnal
❖ Ae albopictus (for DENV) - exophagic, generalist, opportunist (zoonotic risk), day-biter
❖ Ae aegypti (for YFV) - endophilic, endophagic, anthropophagic, day-biter
3. Give an example why (bio)diversity plays a role in MBDs.
❖ During lecture: genetic diversity, breeding site diversity and species diversity
➢ GD: High replication & mutation rates of RNA-viruses result in the emergence of new epidemic variants
adapted to local vector populations = host genotypes and pathogen genotypes can change complementary or
not (sl 17 - coevolution?) + E1-226V mutation in Ae albopictus enhances CHIKV transmission !
➢ BS: different species prefer different breeding sites: various possibilities ranging from natural sites (like tree
holes) to man-made artificial sites (trash, water containers, ..)
■ E.g., Anopheles vs Aedes
➢ SD: each species can have a different pathology, transmission route, reservoir, genetic background, ecology,
behaviour, …
■ E.g., Ae albopictus & Ae aegypti (exophily or endophily; opportunistic zoonotic or anthroponotic)
4. Detailed consequences of global change on MBDs.
❖ Global warming results in the spread of the vectors (e.g., for DENV) to spread to Europe. This in combination with the
changing host/human behaviour as response to the changing climate (e.g., ↑ water collection to survive climate drought)
+ Climate sustainability & example dryness = more breeding sites & interplay MBD
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, Fleas, ticks, mites and lice
1. Fleas and associated diseases
Ecology
❖ Adults: bloodsucking (M/F)
❖ Specificity for a host = ecological specificity
❖ Larvae: detriphagous
❖ Survival during several months without food!
❖ Temp: 22 - 24°C, RH: 80%
Diseases
❖ Plague
❖ Flea-borne/murine/endemic typhus
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Disease 1: Plague - Yersinia pestis
❖ Modern plague originated from middle-age strains, but is not that severe
❖ Rural plague: people handling wild animals
❖ How?
○ Bacilli multiply in the clot induced by the infection in the proventriculus of the flea. When a blocked flea feeds,
thousands of bacilli per bite can be inoculated into the host.
❖ Types?
○ Dog/cat flea ~ Ctenocephalides canis/felis: 0% (no transmission!!)
○ Human flea ~ Pulex irritans 32%
○ Oriental rat flea ~ Xenopsylla cheopis 60%
❖ Current status?
○ Still some cases in Southern Africa, West-Africa, Brazil, Peru, Ecuador, … = Southern Af/Am !!
○ Since the mid-20th century, plague in the US has typically occurred in the rural West (e.g. Illinois)
Disease 2: Endemic or Murine typhus - Rickettsia typhi (avant R. mooseri)
❖ Worldwide distribution
❖ Reservoir in rodents
❖ Primarily transmitted by the rat flea, Xenopsylla cheopis
❖ Secondarily transmitted by the cat flea, Ctenocephalides felis and mouse flea, Leptopsylla segnis
❖ Contamination via bite of an infected flea or by an inoculation of infected flea faeces in the bite wound
❖ Treatment: AB like tetracycline, doxycycline and chloramphenicol
❖ Prevention: rat control
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